Weirdest Electrical Issue I've Ever Encountered

I have a 2003 Ford Focus that I recently aquired from my father. The battery light has been on for a year and he had both the alternator and battery replaced back in April.

When I got the car a week ago, I set out to fix the problem - and did some tests on the electrical systems and found the alternator bad (at this point I didn’t do any in depth tests) so I brought the vehicle over to Sears because the alternator was under warranty. They replaced the alternator and told me that the voltage was still not getting where it neeeded to go (I was in a rush and didn’t do any tests to find out what they meant by that.)

The next day I started to look a little deeper into the problem and discovered the alternator output (at the B-terminal of the alternator) was only putting out 12.1 volts. I took it back to Sears and they tried to tell me that I had some sort of ‘electrical feedback’ affecting the alternator and that they wouldn’t cover a replacement alternator.

I then took the 03 Ford Focus wiring diagram and follwed the factory diagnostic instructions - did voltage drop tests on all the wiring - checked the fuses - hooked up an auto scanner to the OBDII port and found no problems… everythng pointing to the alternator.

Returned to Sears and based on this information got them to replace the alternator again. They replaced it with another alternator (all the alternators the put in were remanufactured.)

With this alternator I’m finding the same problems - the battery light is still on (as it has been for a year) the wiring all appears to be good and, most importantly, the alternator STILL is reading 12.1 volts.

The voltage doesn’t change when revving the engine and when I turn on all loads (lights, high beams, radio, rear defrost etc) the system voltage drops to around 11.5

ANY ideas or thoughts would be greatly appreciated, this is driving me crazy.

Check the ground connections below the air filter box, and the ground connection from the engine to the body. These must be clean and tight. A lot of alternator problems occur with Focus’s because of poor grounds.


Hook up a temporary ground wire directly from the battery to the alternator frame. Check the output now. The built-in regulator may have a “voltage sensing” wire feeding it, How many wires connect to the alternator?

4 Stars for you! I concur!

You didn’t state which engine and model Focus you have but have you considered the possibility of a blown 10 amp fuse in the battery junction box and/or a blown 150+ amps in-line fuse in the alternator main output lead?